Solid state imaging devices, such as a charge coupling device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor are used for various usages, such as a digital still camera, a video camera, or a surveillance camera.
A back-illuminated image sensor can eliminate obstacles to light, such as interconnects between pixels and micro lenses, and therefore can increase the sensitivity of the pixels to incident light and reduce optical shading.
Therefore, development of the back-illuminated image sensor has been promoted in recent years.